Production of chloracrolein



Patented Sept. 16, 1947 UNHD STATES TENT OFFICE PRODUCTION OF CHLORACROLEIN No Drawing. Application August 14, 1945, Serial No. 610,880. In Great Britain July 19, 1944 4 Claims.

This invention relates to a process for the production of chloracrolein.

A process has previously been proposed for the production of chloracrolein by chlorinating acrolein and subsequently recovering hydrochloric acid either by treatment with sodium acetate or by steam distillation, but it suffers from the disadvantages that the yield of chloracrolein is low and that the other reaction products are of little value. It is an object of the present invention to provide a process that gives high yields of chloracrolein and of ethylene.

According to the invention there is provided a process for the production of chloracrolein which comprises pyrolising 5,chlor-2,3-dihydropyran. Ethylene is produced simultaneously and can generally be recovered. The pyrolysis may be effected at a temperature of from 350 C. to

negligible proportions, by working at a lower pass conversion and in the presence of a diluent. It is of course possible by using inert diluents and very low space velocities to attain 100% pyrolysis, but this will not generally be economic.

Good results are obtained by pyrolising vaporised 5,chlor-2,3-dihydropyran at a temperature of 400 C.450 C, employing a space velocity of up to 100 gms. of chlor-dihydropyran per litre of pyrolysis space per hour and a molecular ratio of diluent nitrogen to chlor-dihydropyran of between 2.521 and 1:1.

When higher pyrolysis temperatures are used it is preferred to operate at a higher space velocity and, preferably, to employ a larger proportion of inert diluent.

The results of a series of runs are given in the following table:

Space R?fflOW Y' 16. r i f l d of chlop o rogen 1e 0 Yield of c or 1- use u pro Pyrolysis moles/mole chlorhydroucts as Temp. C. 'gg of chloracrolein ethylsene pyran percentage i dihydrogms. gm pyrolof theoretgm pyran. ised gms. ical 500 C., but is preferably carried out at from 400 C. to 450 C. We have also found that the yield at a given operating temperature can be materially increased by carrying out the reaction in the presence of an inert diluent such as nitrogen, or at reduced pressure. Chloracrolein in a high state of purity can be readily obtained from the products by distillation.

The pyrolysis is eifected, for example, by vaporising 5,chlor-2,3-dihydropyran, passing the vapour through a pyrolysis chamber containing, for example, pumice or silica chips maintained at a .temperature of 400 C. to 450 C. and condensing the products by means of a Water condenser. We have found a pyrolysis chamber of heat-resistant glass to be suitable. Chloracrolein is recovered from the condensate, which also contains unchanged chlordihydropyran, by distillation under reduced pressure, and the ethylene is scrubbed and collected in a gas holder. Although 100 per cent pyrolysis per pass can be achieved when no inert diluents are employed, a greater yield of the desired products is obtained, and the formation of tar is reduced to Example 303 grams of 5,chlor-2,3-dihydropyran were vaporised, and 5'7 grams of the vapour (corresponding to 0.049 litre of liquid) and 10 litres of nitrogen were passed per hour through a pyrolysis zone of 700 mls. volume, comprisng a tube made of glass, packed with pumice and maintained at 400 C. by means of an electrically heated jacket. This rate corresponds to a liquid space velocity of 0.07 litre of chlordihydropyran 5 per hour per litre of reaction zone. The products of the reaction were condensed by means of a water condenser and the ethylene evolved was collected and its volume measured. The liquid condensate, amounting in weight to 265 grams, was distilled at reduced pressure and yielded 672 grams of chloracrolein and 169.8 grams of unchanged chlordihydropyran. The volume of ethylene obtained was 17 litres; which corresponds to 65 grams of chloracrolein.

We claim:

1. A process for the production of chloracrolein which comprises pyrolysing 5,chlor-2,3-dihyd'ro-' pyran in the vapour phase at a temperature of 350 C.500 C.

2. A process for the production of chloracrolein which comprises pyrolysing 5,chlor-2,3-dihydropyran in the vapour phase at a temperature of 400 C.-450 C. in the presence of an inert diluent employed in a proportion of from 2.5 moles to 1 mole per mole of 5,chlor-2,'3-dihydropyran.

3. A process for the production of chloracrolein which comprises pyrolysing 5,chlor-2,3-dihydro- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,365,623 Bremner et a1. Dec. 19, 1944 2,387,366 Toussaint Oct. 23, 1945 

